With the ever-increasing need for high-speed data signal processing and higher clock speed microprocessors, comes a need to pass high-speed signals through electrical connectors in a system. Also, because of electrical performance concerns and the desire to make devices smaller, comes a need to pass a greater number of high-speed signals through the electrical connectors in a system.
To address these needs, electrical connectors have been developed for connecting peripheral devices on substrates such as printed circuit boards to a system through a card edge receiving electrical connector. These connectors have been developed for connecting to conductive pads disposed along an edge of the printed circuit board. Because of the need for higher density interconnections in these systems, pads are sometimes disposed along the printed circuit board edge in a plurality of rows. For example, U.S. Pat. No. 5,071,371 shows a card edge connector for contacting two parallel rows of pads along a printed circuit board. U.S. Pat. No. 4,298,237 shows a variation of a card edge connector for contacting three parallel rows of contact pads along an edge of a printed circuit board.
A problem exists with these connectors in systems where it is desirable to have a large number of signals passing through such a connector in a minimum space. In order to reduce the space occupied by the connector, it is necessary to have an extremely narrow pitch for the contacts. This translates into less space between each adjacent contact and causes degradation of the electrical signals passing through the connector. The degradation is caused by a cross talk effect between adjacent contacts. As the contacts are moved closer to each other, each contact may be effected by an electromagnetic field emanating from an adjacent contact. The contact receiving the electromagnetic field will have a degraded electrical signal. This is known as cross talk. in order to reduce this effect, ground contacts are typically strategically positioned throughout the connector so that cross talking signals couple to ground instead of coupling to adjacent signals. Since the addition of more ground contact increases the size of the electrical connector it is desirable to select an optimum minimum number of ground contacts and strategically place these contacts to reduce the cross talk effect.
It is therefore desirable to form a dense electrical interconnection between a card edge and a second substrate, which allows passage of many high-speed signals.